Polyethylene terephthalare resins have been widely used as fibers, films, molding materials and the like due to excellent mechanical and chemical properties. However, the polyethylene terephthalate resins have an intramolecular ester linkage, which would be hydrolyzed when the resins are exposed to a high temperature and high humidity condition for a long period of time, thereby the mechanical properties or moist heat resistance thereof being lowered. For that reason, the polyethylene terephthalate resins are not suitable for a specific field where the moist heat resistance is required, such as for an electric rice-cooker. In order to improve such defect, for example; Japanese Patent Laid-Open No. 46-5,389 describes a method for blending compounds having an intramolecular carbodiimide group to polyethylene terephthalate resins to prevent a decrease in strength thereof. Further, Japanese Patent Publication No. 47-13,860 describes that a polyfunctional compound such as an epoxy compound is added to polyethylene terephthalate to increase molecular weight, thereby improving impact strength thereof.
However, the compound having an intramolecular carbodiimide group, in spite of an expensive price, should be added in a considerably large amount to polyethylene terephthalate to sufficiently exhibit an improvement in the moist heat resistance. On the other hand, although it is possible to improve the moist heat resistance to a certain extent by adding a polyfunctional epoxy compound to polyethylene terephthalate, a resin thus prepared has poor fluidity and is not adaptable to injection molding to form thin-walled products. Further, when a nucleating agent of organic acid metal salts is added to a polyethylene terephthalate resin to accelerate the rate of crystallization for the purpose of improving moldability of the resin, the moist heat resistance becomes so deteriorated that the resin can not be applied to a field where such resistance is required.
As a result of an intensive series of studies by the present inventors to solve the above mentioned problems, it has been found that a resin of improved fluidity, moist heat resistance and mechanical strength can be obtained by adding a compound having not less than two intramolecular epoxy groups and none of intramolecular ester linkage therein, and/or a carbodiimide compound (B), and if necessary, a fibrous reinforcing material (C) to a polyethylene terephthalate resin (A) polymerized with a germanium catalyst.
It has also been found that a crystallization rate of a polyethylene terephthalate resin can be improved without losing the above mentioned properties by adding a predetermined amount of an inorganic nucleating agent (E), thereby enabling high cycle molding.
Further, it has been found that a molded article, which exhibits satisfactory surface characteristics even when molding with a mold of a low temperature, can be obtained by adding a predetermined amount of a specific block copolymer (D), with the above mentioned properties being kept.
The present invention has been accomplished on the basis of these results as described above.